Display device with watermark area and non-watermarks area

ABSTRACT

The present invention is directed to display devices comprising a watermark area and a non-watermark area. The display cells in the watermark area have widths of the partition walls, heights of the partition walls, top opening shapes or display cell sizes which are different from those of the display cells in the non-watermark area. The watermark aims to protect against counterfeiting or to be used for decoration purposes. The watermark is visible at certain viewing angles and/or under certain lighting conditions and it does not interfere with displaying of the regular images.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.13/896.232, filed May 16, 2013 (Publication No. 2013/0321744, now U.S.Pat. No. 9,470,917 issued Oct. 18, 2016), which claims priority to U.S.Provisional Applications Nos. 61/660,372, filed Jun. 15, 2012; and61/653,210, filed May 30, 2012; the contents of which are incorporatedherein by reference in their entirety.

The entire contents of all U.S. patents and published and copendingapplications mentioned below are herein incorporated by reference.

BACKGROUND OF INVENTION

The present invention is directed to a display device wherein theviewing side of the display device has a watermark area and anon-watermark area and the display cells in the watermark area aremodulated to be distinguishable from the display cells in thenon-watermark area. The display device comprising the watermark featureis useful for protecting against counterfeiting or decoration purposes.

U.S. Pat. Nos. 6,930,818 and 6,795,138 disclose image display devicesbased on the microcup technology. The patents describe the manufactureof microcups as display cells. The microcups are then filled with adisplay fluid. The top openings of the microcups may have the same sizeand shape and such microcups spread across the entire display surface.

SUMMARY OF INVENTION

The first aspect of the present invention is directed to a displaydevice comprising display cells wherein the viewing side of the displaydevice has a watermark area and a non-watermark area and the displaycells in the watermark area are modulated to be distinguishable from thedisplay cells in the non-watermark area.

In one embodiment, the walls of the display cells in the watermark areahave a different width than the walls of the display cells in thenon-watermark area.

In one embodiment, the walls of the display cells in the watermark areaare thicker than the walls of the display cells in the non-watermarkarea.

In one embodiment, the walls of the display cells in the watermark areaare thinner than the walls of the display cells in the non-watermarkarea.

In one embodiment, the walls of the display cells in the watermark areaare at least about 5% thicker or thinner than those in the non-watermarkarea.

In one embodiment, the walls of the display cells in the watermark areahave different thickness.

In one embodiment, the wall of at least one side of a display cell inthe watermark area has varying thickness.

In one embodiment, the walls of the display cells in the watermark areahave a different height than the walls of the display cells in thenon-watermark area.

In one embodiment, the display cells in the watermark area have adifferent shape than the display cells in the non-watermark area.

In one embodiment, the display cells in the watermark area have morethan one type of shape.

In one embodiment, the display cells in the watermarks area have adifferent size from the cells in the non-watermark area. For example,the cells in the watermark area may be at least twice as large (in bothlateral dimensions) as the cells in the non-watermark area.Alternatively, the cells in the watermark area may be not more than onehalf the size of the cells in the non-watermark area.

In one embodiment, the display device is a reflective type of displaydevice.

In one embodiment, the display device is a transmissive type of displaydevice.

In one embodiment, the display device is a transreflective type ofdisplay device.

In one embodiment, the display device is an electrophoretic display.

In one embodiment, the display device is a liquid crystal display.

In one embodiment, the display device further comprises a color layer onthe non-viewing side of the display device. The color layer may be asealing layer, an adhesive layer or an electrode layer.

Another aspect of the present invention is directed to a display devicecomprising display cells separated by partition walls wherein at leastone parameter of the display cells in the watermark area is modulatedwith at least two variations which are different from that parameter inthe non-watermark area. In one embodiment, the parameter is thepartition wall height. In another embodiment, the parameter is thepartition wall width. In a further embodiment, the parameter is theshape of the display cells.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 depict top view of display devices.

FIG. 3 shows a watermark area in which the walls of the display cellsare thicker or wider than those in the non-watermark area.

FIG. 4 shows the wall thickness in the watermark area may vary.

FIG. 5 shows the thickness of the wall on at least one side of a displaycell may vary.

FIG. 6 shows a watermark area in which the shape of the display cells isdifferent from that in the non-watermark area.

FIG. 7 shows a cross-sectional view of a display panel.

FIG. 8 shows a watermark having different color intensities.

FIG. 9 shows a cross-sectional view of a display panel, which hasdifferent heights of partition walls 90 a in watermark area (W) andnon-watermark area (nW).

FIG. 10 shows a watermark area in which the walls of the display cellsare thinner than those in the non-watermark area.

DETAILED DESCRIPTION

The present inventors have now found that a watermark feature may beadded to a display device, which watermark is useful to protect againstcounterfeiting when a security measure is required for the displaydevice. In addition, the watermark may also be used for ornamentaldesign/decoration purposes.

The watermark feature may be achieved by modulating (i.e., altering) atleast one parameter of the display cells, in the watermark area.

FIGS. 1 and 2 depict top views of a display device. In the two examples,the display cells have a square or hexagonal top opening, respectively.The entire surface of the display device may be divided into the displaycell area (shaded) and the partition wall area (11 and 21). The displaycell area comprises a plurality of display cells (12 and 22) which aremicro-containers filled with a display element, such as a display fluid.

Each individual display cell usually has a cell width (cw) smaller than300 μm. The cell width, in the context of this application, is definedas the distance between two opposing parallel sides of a display cell.

Because of their small size and uniform shape, the individual displaycells are barely perceivable by naked eyes. Therefore such a displaydevice can display images without the grid-like feel.

The wall width (ww) of the partition walls is usually in the range ofabout 5 to about 30 μm. When referring to partition walls in thisapplication, “width” and “thickness” and “wider” and “thicker” are usedinterchangeably.

Therefore, display devices prepared by the microcup technology (asdescribed in U.S. Pat. Nos. 6,930,818 and 6,795,138) are most suitablefor the present invention because the microcup-based display cells aresufficiently small and they may be formed to have a uniform size andshape. However, the scope of the invention may also extend to anydisplay device as long as it has display cells which are sufficientlysmall and have well-defined sizes and shapes that may be pre-determinedbefore manufacture.

The microcup-based display cells may be manufactured by any of theprocesses (such as microembossing) described in the US patentsidentified above. Briefly the modulated parameter(s) may be built-in inthe male mold to be used for forming the microcup-based display cells inan embossing process.

The display element filled in the display cells may be anelectrophoretic fluid comprising charged pigment particles dispersed ina solvent or solvent mixture. An electrophoretic display typicallycomprises two plates with electrodes placed opposing each other. When avoltage difference is imposed between the two electrodes, the pigmentparticles in the display fluid migrate to one side or the other causingeither the color of the pigment particles or the color of the solventbeing seen from the viewing side.

Alternatively, an electrophoretic fluid may comprise two types ofcharged pigment particles of contrasting colors and carrying oppositecharges, and the two types of the charged pigment particles aredispersed in a clear solvent or solvent mixture. In this case, when avoltage difference is imposed between the two electrode plates, the twotypes of the charged pigment particles would move to opposite ends (topor bottom) in a display cell. Thus one of the colors of the two types ofthe charged pigment particles would be seen at the viewing side of thedisplay cell.

While electrophoretic display is specifically mentioned, it isunderstood that the present application is applicable to other types ofdisplay device as well, such as other types of reflective display deviceor transmissive and transreflective display devices, including liquidcrystal display devices.

The watermark created according to the present invention is visible atcertain viewing angles and/or under certain lighting conditions. Thewatermark would not interfere with the desired regular images displayed(based on movement of charged pigment particles in a solvent or solventmixture in an electrophoretic display, for example).

In one embodiment of the present invention, the width of the partitionwalls of the display cells is modulated. As shown in FIG. 3, the displaydevice has a watermark area (W) and a non-watermark area (nW). In thewatermark area (alphabet “E”), the partition walls of the display cellsare wider or thicker than those in the non-watermark area.

In another embodiment, the partition walls in the watermark area may bethinner than those in the non-watermark area.

In general, the width of the partition walls in the watermark area maybe at least about 5% thicker or thinner than those in the non-watermarkarea. It is noted that the wall thickness in some of the drawings isexaggerated for clarity.

In another embodiment as shown in FIG. 4, the thickness of the partitionwalls in the watermark area may vary. In this case, the differences inthe wall width can generate different levels of color intensity todisplay a grey-scale-like image for the watermark.

In a further embodiment as shown in FIG. 5, the wall thickness may varywithin the partition wall on at least one side of a display cell. Byvarying the wall thickness on at least one side of a display cell, itmay create a different optical effect in the watermark area to cause itto be distinguished from the non-watermark area.

In yet a further embodiment, the shape of the display cells may be amodulating parameter. In an example as shown in FIG. 6, the displaycells in the watermark area (alphabet “O”) have a different shape (i.e.,triangle) than those in the non-watermark area (i.e., square). Theshapes in the watermark area or the non-watermark area are not limitedto triangle or square. They may be any regular shapes or irregularshapes as long as the shape of the display cells in the watermark areais different from that in the non-watermark area. It is also possiblethat not all of the display cells in the watermark area have the sameshape. The term “shape”, in this embodiment of the invention, refers tothe shape of the top opening of the display cells.

In yet a further embodiment (not illustrated in the drawings), the sizeof the display cells may be a modulating parameter. For example, in amodification of the display shown in FIG. 6, instead of the displaycells in the watermark area being (notionally) obtained from the cellsin the non-watermark area by dividing each rectangular cell diagonallyto produce two triangular cells, each cell may be divided by wallsparallel to its original walls to divide each cell into a 2×2, 3×3 . . .etc. array of cells which share the shape of the cells in thenon-watermark area but are smaller in both lateral dimensions.Alternatively, the cells in the watermark area may be made larger thanthose in the non-watermark area by removing partition walls betweencells in the watermark area, thus combining four, nine etc. cells in thewatermark area into a single cell two or three etc. times as large inboth lateral dimensions as the cells in the non-watermark area.

The different shapes of the display cells in the watermark area may beachieved by a number of methods. Certain methods are described in U.S.patent application Ser. No. 13/765,588, the content of which isincorporated herein by reference in its entirety. Briefly, the design ofthe different shape of the display cells (e.g., microcups) in thewatermark area may be achieved by removing partition walls ofnon-altered display cells and replacing the removed partition walls withnew partition walls. Alternatively, the design of the different shape ofthe display cells (e.g., microcups) in the watermark area may beachieved by independently shifting apex points of non-altered displaycells within a defined area, and reconnecting the shifted apex points.Utilizing these design methods, the display cells in the watermark areamay have different shapes (i.e., randomized).

In yet a further embodiment, the height of the partition walls of thedisplay cells may be a modulating parameter for the watermark area.

The watermark is not limited to characters, numbers or geometric shapes.It may also be complex images such as pictures with grey levels.

As stated above, the watermark may only be visible in a display deviceat certain angles or under strong lighting conditions; and it usuallywill not be seen in the normal display mode so that the quality of theregular images displayed is not affected.

FIG. 7 shows a cross-sectional view of a display panel. A plurality ofdisplay cells (70) filled with a display fluid, are sandwiched betweentwo electrode layers (71 and 72). As discussed above, the width of thedisplay cell walls (70 a) may be modulated to form a watermark. In thecase of microcup-based display cells, the filled microcups are sealedwith a sealing layer (73). The electrode layer (71) is laminated overthe filled and sealed microcups, optionally with an adhesive layer (74).This display panel is viewed from the side of the electrode layer (72).

In one embodiment of the present invention, a color layer may be addedto enhance the viewing of the watermark. The color layer is on the sideopposite of the viewing side. In other words, the color layer is on thenon-viewing side.

When a color layer is present, the watermark can be better seen evenwhen the image is at the full black or white color state.

The color layer may be achieved by making the sealing layer (73), theadhesive layer (74) or the electrode layer (71) colored. For example, apigment or dye material may be added to a sealing composition oradhesive composition to cause the sealing or adhesive layer to becolored. The electrode layer may be colored (e.g., a metallic shade).

FIG. 9 shows a cross-sectional view of a display panel. A plurality ofdisplay cells (90) filled with a display fluid are sandwiched betweentwo electrode layers (91 and 92). The filled display cells are sealedwith a sealing layer (93). In one embodiment, the sealing layer is acolor layer. The heights of partition walls (90 a) in a watermark (W)are different from those in the non-watermark area (nW).

In another aspect, each modulating parameter, according to the presentinvention, may have one or more variations in the watermark area fromthe non-watermark area. For example, the wall widths of the displaycells may be modulated and the display cells in the watermark area mayhave one or more wall widths which are different from that in thenon-watermark area. In another example, the wall heights of the displaycells may be modulated and the display cells in the watermark area mayhave one or more wall heights which are different from that in thenon-watermark area. In another example, the shapes of the display cellsmay be modulated and in this case, the display cells in the watermarkarea may have one or more shapes which are different from that in thenon-watermark area.

When there are two or more variations for a modulating parameter in thewatermark area, the watermark may show different color intensities. Asshown in FIG. 8, there are different color intensities in the watermarkarea (i.e., a logo and the word “SiPix”) because there are more than onewall widths which are different from that in the non-watermark area.

While the present invention has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particularsituation, materials, compositions, processes, process step or steps, tothe objective and scope of the present invention. All such modificationsare intended to be within the scope of the claims appended hereto.

1. A display device comprising display cells filled with a displayfluid, each of the display cells having partition walls for separatingthe display cells and wherein the display device has a watermark areaand a non-watermark area and the display cells in the watermark areahave a different size from the display cells in the non-watermark area.2. The display device of claim 1, wherein the walls of the display cellsin the watermark area are at least twice as large in both lateraldimensions as the display cells in the non-watermark area.
 3. Thedisplay device of claim 1, wherein the walls of the display cells in thewatermark area are not more than one half the size of the display cellsin the non-watermark area.
 4. The display device of claim 1, which is areflective type of display device.
 5. The display device of claim 1,which is a transmissive type of display device.
 6. The display device ofclaim 1, which is a transreflective type of display device.
 7. Thedisplay device of claim 1, which is an electrophoretic display.
 8. Thedisplay device of claim 1, which is a liquid crystal display.
 9. Adisplay device comprising display cells separated by partition wallswherein at least one parameter of the display cells in a watermark areais modulated with at least two variations which are different from thatin a non-watermark area.
 10. The display device of claim 9, wherein theparameter is the partition wall height.
 11. The display device of claim9, wherein the parameter is the partition wall width.
 12. The displaydevice of claim 9, wherein the parameter is the shape of the displaycells.
 13. The display device of claim 1, further comprising a colorlayer on the non-viewing side of the display device.
 14. The displaydevice of claim 13, wherein the color layer is a sealing layer.
 15. Thedisplay device of claim 13, wherein the color layer is an adhesivelayer.
 16. The display device of claim 13, wherein the color layer is anelectrode layer.